Numerical Comparison of Protective Measures for Mitigating the Impact of Vacuum Preloading on Surrounding Soil

• Cement–soil mixing pile isolation walls significantly reduce both lateral and vertical deformation outside the vacuum-preloaded zone by blocking pore-pressure transmission and providing high structural stiffness. • Wall depth and width are dominant factors: deeper walls mainly improve vertical settlement control, while wider walls strengthen lateral restraint via increased bending stiffness. • Stress relief trenches effectively reduce lateral displacement by providing a deformable buffer zone and dissipating pore-pressure gradients, though they offer weaker vertical settlement control than isolation walls. • Trench geometry controls performance: increasing trench depth enhances lateral impact-range reduction, while increasing width primarily improves vertical settlement moderation, both with diminishing returns. • Comparative performance shows isolation walls provide comprehensive protection, especially for vertical settlement whereas trenches serve as a cost-effective alternative when lateral deformation control is the primary design need. Vacuum preloading is widely used for soft soil improvement due to its efficiency in accelerating consolidation and enhancing foundation strength. However, its application inevitably induces lateral soil deformation, pore-pressure redistribution, and ground settlement outside the reinforced zone, which may adversely affect adjacent structures and the environment. To address these challenges, this study systematically investigates protective measures designed to mitigate the environmental impacts of vacuum preloading. A coupled numerical consolidation model was developed using a Mohr–Coulomb constitutive framework with pore-pressure diffusion, incorporating realistic boundary conditions, vacuum load history, and mesh refinement near protective structures. Two representative protective measures; cement-soil mixing pile isolation walls and stress relief trenches were analyzed under varying geometrical configurations. The effectiveness of each measure was quantified through displacement fields, pore-pressure contours, and influence range evaluations, supported by parametric studies and grey relational analysis to determine dominant factors. The results demonstrate that cement-soil mixing pile walls provide strong vertical and lateral protection by blocking pore-pressure transmission and mobilizing high bending stiffness, with performance highly sensitive to wall depth and width. Stress relief trenches, in contrast, primarily attenuate lateral displacement through stress redistribution and hydraulic buffering, with depth exerting a stronger influence than width. Comparative analysis highlights that while walls achieve superior overall isolation, trenches offer a cost-effective and easily implemented alternative in cases where lateral deformation control is prioritized. Therefore, this study provides new insights into the mechanisms, governing equations, and parametric sensitivities of protective measures against environmental impacts of vacuum preloading. The findings form a practical basis for selecting and optimizing protection strategies in large-scale ground improvement projects, thereby enhancing both engineering reliability and environmental safety.